<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Promise 封装 AJAX</title>
    <link crossorigin='anonymous' href="https://cdn.bootcss.com/twitter-bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
</head>
<body>
<div class="container">
    <h2 class="page-header">Promise 封装 AJAX 操作</h2>
    <button class="btn btn-primary" id="btn">点击发送 AJAX</button>
</div>
<script>
    //接口地址 https://api.apiopen.top/getJoke
    //获取元素对象
    const btn = document.querySelector('#btn');

    btn.addEventListener('click', function(){
        //创建 Promise
        const p = new Promise((resolve, reject) => {
            // 1、实例xhr对象
            let xhr = new XMLHttpRequest()
            // 2、初始化
            xhr.open('GET','https://api.apiopen.top/getJoke')
            // 3、 发送请求
            xhr.send()
            // 4、处理响应
            xhr.onreadystatechange = ()=>{
                if(xhr.readyState == 4){
                    if(xhr.status >= 200 && xhr.status <= 300){
                        resolve(xhr.response)
                    }else{
                        reject(xhr.status)
                    }
                }
            }
        });
        //调用then方法
        p.then(value=>{
            console.log(value);
        }, reason=>{
            console.warn(reason);
        });
    });
</script>
</body>
</html>